She only did what we all, deep inside, would love to.
You can hold that against her and adhere to a twisted moral and ethical code which helps no one. Physical pleasure can exist outside an intimate relationship. Call it 'assisted self-service', if you wish.
If she honestly regrets, make up. All she did was kiss, so what? Satisfying primal lust through watching porn is, on an abstract level, not all that different from having loveless sex. I don't know, and don't care if you watch porn, but know that only the truly innocent should cast the first stone.
Or you could dump her and move on. She's not The One, she's not irreplacable.